With rapid progress in the information industry, sputtering target materials used for fabrication of information industrial equipment are used in large quantities. It is well known that an optimum method for manufacturing such target materials is a sintering process of a high purity metal powder raw material. For this reason, demand for high purity and melting point metal powder is increasing while, owing to high functionality of the information equipment, increase in purity is required.
Moreover, in sintering and manufacturing a target in a near net shape, spheroidizing the powder described above is necessary while a high purity copper (‘Cu’) powder is required for use as a conductive paste or a penetrator liner or the like.
A method of manufacturing a high purity Cu powder, which includes repeatedly conducting chemical wet separation and refinement of ore, preparing a high purity intermediate oxide or compound, decomposing the oxide or compound, and conducting hydrogen reduction thereof, thereby fabricating a metal powder, has been generally known in the art.
Korean Laid-Open Patent Publication No. 10-2004-0097364 describes a wet-prepared powder wherein oxygen content is considerably high, i.e., 2000 ppm or more, and impurity residue remains in oxide, thus causing a restriction in high refinement and significant problems in environmental contamination due to various solutions and controlling (managing) a particle diameter of the prepared powder to 1 μm or less.
Compared to a wet separation method entailing the above problems, Korean Laid-Open Patent Publication No. 10-2005-0033721 describes a method for manufacturing carbon nanotubes using DC thermal plasma at a very high temperature. A DC plasma technique cannot avoid mixing of impurities due to corrosion of an electrode, thus causing a difficulty in fabricating a high purity metal powder.
Meanwhile, a method for manufacturing a high purity powder using RF thermal plasma has been disclosed in Japanese Laid-Open Patent Publication No. 2001-342506 (hereinafter, ‘cited invention A’) and Japanese Laid-Open Patent Publication No. 2002-180112 (hereinafter, ‘cited invention B’).
According to cited invention A, a metal block is milled to produce a powder and the powder is treated through thermal plasma treatment to form a high purity metal powder such as tungsten (W), molybdenum (Mo), tantalum (Ta), ruthenium (Ru), etc. On the other hand, cited invention B describes a high purity metal powder such as tungsten (W), molybdenum (Mo), tantalum (Ta), ruthenium (Ru), etc., fabricated by treating a high melting point metal oxide or metal compound having an average particle diameter of 10 to 320 μm, through RF thermal plasma while introducing hydrogen.
The foregoing cited inventions are characterized in that high melting point metal is neither molten nor vaporized while passing the high melting point metal through thermal plasma, however, impurities having a relatively low melting point are evaporated and blown in a cyclone, to thus attain high refinement. However, for copper (Cu) having a relatively low melting point, since not only impurities but also a raw powder may be evaporated and blown off, a high purity Cu powder cannot be manufactured according to the methods described in the cited inventions.